This invention relates generally to methods and apparatus for plating wafers, substrates and other articles, and in particular, to methods and apparatus of configuring the fluid dynamics and electrostatics of a plating process in order to provide improved uniformity in plating deposition, improved plating rates, and improved step coverage of via holes.
Because of recent technological advancements in the fields of computers and telecommunications, there has been a substantial increase in demand for xe2x80x9chigh techxe2x80x9d products. Not only do consumers want more sophisticated computer, telecommunication and other xe2x80x9chigh-techxe2x80x9d systems, they want it at a more economical costs. Because of this consumer desire, high tech industries are gearing their manufacturing techniques to produce products that are made as economical as possible, with improved performance and reliability.
One of the backbone industries supporting many high tech industries, including the computer and telecommunication fields, involves the manufacturing of semiconductor wafers. Semiconductor wafers are used extensively for the manufacturing of integrated circuits, semiconductor devices, and other circuits and/or components. The manufacturing of an integrated circuit or device typically comprises several manufacturing stages, including processing the semiconductor wafer to form the desired circuits and/or devices, forming a copper seed layer on the base plate of the semiconductor, plating the copper seed layer with a layer of copper having a desired thickness, and dicing the wafers in order to form separate integrated circuits and/or components. The invention described herein involves the plating aspect of the overall integrated circuits/devices manufacturing process.
Because of high tech industries"" need for manufacturing techniques that economically produce products that have improved performance and reliability characteristics, this need is also a driving force in the field of plating semiconductor wafers. In terms of performance, it is desired for a method and apparatus for plating semiconductor wafers that achieves improved uniformity of the plating deposition across the surface of the wafer. In terms of reliability, it is desired for a method and apparatus for plating semiconductor wafers that accomplishes the desired plating of the semiconductor wafer, without subjecting the wafer to unnecessary harsh environments. In terms of manufacturing costs, it is desired for a method and apparatus for plating semiconductor wafers that accomplishes the desired plating of the semiconductor wafer in a relatively fast manner.
These needs are satisfied with the method and apparatus of plating wafers, substrates and other articles in accordance with the invention as described hereinafter.
A first aspect of the invention is a method and apparatus for plating a wafer that is particularly useful in improving the plating rate. This aspect of the invention comprises the technique of immersing a wafer in a bath of plating fluid and continuously directing fresh plating fluid towards the surface of the wafer. The directing of plating fluid towards the surface of the wafer increases the ion concentration gradient between the cathode-contacted wafer and the anode. The current between the anode and the cathode is proportional to the ion concentration gradient at the surface of the wafer. The plating rate is also proportional to the current. Accordingly, increasing the ion concentration gradient by continuously directing plating fluid towards the surface of the wafer, increases the current, and therefore increases the plating rate. Thus, a relatively high plating rate can be achieved by directing plating fluids towards the wafer, while the wafer is immersed in a bath of plating fluid.
A second aspect of the invention is a method and apparatus for plating a wafer that is particularly useful in plating high aspect ratio via holes. This aspect of the invention comprises the technique of immersing a wafer with the side to be plated facing up in a bath of plating fluid. By immersing a wafer in a bath of plating fluid, any pockets of air or gas formed within via holes rise due to buoyancy and therefore, move out of the via hole. Accordingly, the absence of trapped pockets of air or gas within via holes allows the plating ions to better adhere to the walls of via holes without hindrance if, otherwise, the trapped air or gas were present.
A third aspect of the invention is an apparatus and method for plating a wafer that is particularly useful in improving the uniformity of the plating deposition across the surface of a wafer. This aspect of the invention comprises continuously effecting random plating fluid flow in the horizontal directions (i.e. x-y directions) within a bath of plating fluid. The random horizontal fluid flow in a plating fluid bath reduces the of the occurrences of relatively long horizontal fluid flow path. Long horizontal fluid flow path forms uneven plating of the surface of a wafer. Accordingly, effecting random horizontal plating fluid flow helps in improving the uniformity of the plating thickness across the surface of the wafer.
A fourth aspect of the invention is an apparatus and method for plating a wafer that is particularly useful in improving the uniformity of the plating deposition across the surface of a wafer. This aspect of the invention comprises configuring the electrostatic field lines between the anode and the cathode so that a more uniform current distribution across the surface of the wafer is formed. A substantially uniform plating current across the surface of the wafer provides for a substantially uniform thickness of the plating deposition across the surface of the wafer. In the preferred implementations, the electrostatic fields can be configured by providing a selectively shaped anode and/or cathode, by providing an electrostatic shield between the anode and the cathode, and/or providing an electrically conductor between the anode and cathode that can alter the electrostatic field in response to a control voltage.
A fifth aspect of the invention is an apparatus and method for plating a wafer that is particularly useful in improving the uniformity of the plating deposition across the surface of a wafer, improving the plating rate, and minimizing cathode contact damage to the wafer. This aspect of the invention comprises providing an electrically conductive liquid in order to effectuate the cathode contact to the surface of the wafer. In the preferred embodiment, the conductive liquid comprises a mixture of sulfuric acid and de-ionized water. Preferably, the conductive liquid is supported by an annular channel configured so that the conductive liquid makes contact to the perimeter region (e.g. exclusion zone) of the wafer surface. Because the conductive liquid provides a continuous and uniform contact to the wafer, the uniformity of the plating deposition across the surface of the wafer is improved. Because the conductive liquid makes a continuous contact, a large surface contact area is achieved for providing increased current capacity which improves the plating rate. Because the cathode connection to the wafer is accomplished by a liquid, this minimizes mechanical damage to the wafer.
A sixth aspect of the invention is an apparatus and method for plating a wafer that is particularly useful in preventing acidic damage to the copper seed layer of the wafer during the initial stage of forming the plating fluid bath. This aspect of the invention comprises providing a secondary anode near the surface of the wafer that is energized with a positive voltage. The positive voltage activates the plating fluid that is initially introduced into the bath, and prevents the acidic properties of the plating fluid from damaging the copper seed layer of the wafer. Once the primary anode is immersed, the positive voltage on the secondary anode is removed.
A seventh aspect of the invention is an apparatus and method for plating a wafer that is particularly useful in improving the uniformity of the plating deposition across the surface of the wafer when the wafer is initially being plated. When the wafer is initially being plated, the surface resistance of the wafer is high due to the high resistive properties of the seed layer (e.g. copper seed layer). As a result, more of the plating is deposited where the cathode makes contact to the wafer (e.g. at the perimeter of the wafer). This aspect of the invention comprises providing a secondary cathode situated near the cathode contact of the wafer to reduce the plating rate near the cathode contact in response to a control voltage that is more negative than the cathode. The more negative voltage on the secondary cathode diverts plating ions that would otherwise be deposited near the cathode contact. The control voltage is selected to improve the uniformity of the plating deposition across the surface of the wafer.
Additional aspects of the invention include (1) an apparatus and method for initial loading of a wafer; (2) an apparatus and method for wafer alignment and final loading; (3) an apparatus and method for supporting a wafer; (4) an apparatus and method for cathode alignment; (5) an apparatus and method for cathode contacting a wafer; (6) an apparatus and method of draining the plating fluid bath; (7) an apparatus and method of drying an anode; (8) an apparatus and method of rinsing a wafer after plating; (9) an apparatus and method of drying a wafer; (10) an apparatus and method of draining fluids from the plating apparatus; (11) an apparatus and method of controlling and disposing of fumes; (12) an apparatus and method of unloading a wafer; and (13) an apparatus and method of cleaning the plating apparatus.